Controlling polymerization reactions



otentcd Feb. 14, 1950 CONTROLLING POLYMEBIZATION REACTION 8 James H. Young, Niagara Falls, N. Y., ascignor to E. I. du Pont de Nemours & Company, Wil- 11, Del., a corporation of Delaware No Drawing. Application May 22, 1945. Serial No. 595,260

3Claims.

s invention relates to the preparation of polymers. More specifically, the invention relater to the formation of polymers from polymerizohle monomers catalyzed by peroxides or oxygen releasing materials.

it is known that such polymers vary in properties and such systems vary in speed of polymerization when the catalyst concentration is varied. Because of the small amounts of catalysts used and! the large amounts of polymers, monomere, dispersing agents and modifiers often present, chemical tests for following the catalyst concentration are difilcult to maize and the results unreliable.

is especially true for certain recently prooocccl one very active polymee systems in which a neroxygen cornponncl is promoted with o reducing agent.

olilect oi" this invention is to provide a lneono methorl for controlling peroxide cai'onolymerizations. i-l iin'ther ohlect h to Zero hoe iinorovetl polymers hy means of n tievice so regulates the system thot polymer lorlnotion proceeds smoothly oncl erenly.

These objects are aecornolmlierl Toy oontinuowly nieocorlno end if desirable regulation the amount of cotolyst present with siritohle oxidation-reclinetlon electrodes and a potentiometer or pctentl. oiioetric controller.

invention may he imther by was then +110 mv. 2 drops of 0.0095 molar ferric ammonium sulfate was also added as an activator.

Polymerization started immediately raising the temperature from 246 to 441 C. in six minutes. At this point, there was no further polymertion. The potential was 440 mv. and the pH was l.'l. Vinyl acetate was added and the potential remained at no mv. There was no polymerization. The high potential having indicatecl that hydrogen peroxide was present in excess, l ml. oi 0.2 m. sulioxylate was added. The notentlol was 90 mv. Polymerization started immediately raising the temperature from 30.8 C. to 51.3 G. in minutes. The potential was then to mv. illlltl after adding vinyl acetate, it was mv. l lo polymer formerl. The low potential indicated an excess of reclucineagent. Accordingly, it oi on molar H2O; was aclolerl. The pctentiol lilllllll rllately rose from so to tilt and! gradually to til-ll chewing only at small amount oi snlfoxylotc hall teen present, anti so another i ml. of 2 molor onylote was oolcleol. The potential was "it? and nolymerizotion otartecl at once.

Economic if lfhe following; table shows syetenis to which the methoclhoo been applied at in Exam ne i, so as to maintain conditions clesirahle for col olent polymer iortion, irsiinz electrorleo, nlatioum anti a calomel hell-cell.

Monomer Systems PH Ruse (Jotalyci; llosmtiny POtC-Eltiil] Henge Vinyl acetate cllsoerscrl in water Methyl methocrylato in water l to 5 lto5 Hydrogen peroxide and ascorbic acid peroxide and zinc formaldehyde colloxy About +100 to +251] inv. About 0 to +200 mv.

Vinyl cyanide in water some About to to +158 my.

Vinyl acetate in water Ammonium pereulioio and sodium bizmlfltem" About +5!) to +230 my.

Vinyl moron water Tertiary bctyi hydropemxide and zinc ionnal- About to +159 my.

dohydo snlloxyloto. the lollowh'ly one-romeo. The invention is not restricted to the fore rm m ing -11 lmnles, but may he onolierl to the 1 5 nolerization oi other oolymerlrohle mono lll nil. oi vinyl acetate Woo ernrllrlfleci in ml.

oi" water with 63.5 ml. ilviter AD (9, commercial lone choin enllonateel alcohol) as dispersing nyent. ll. hare platinum wire spiral and a calomel cell connected to a potentiometer were used on electrodes to measure the oxidation-reduction potential oi the emulsion.

its o reducing iormolrlehyele sulfoxylate was added. Themtentiel was -lll mv. 1.0 ml. of 0.2 molar hydrogen oerorlele was added on catalyst. o notent promoter 31.0 ml. of 0.2 molar zinc olec compounds having the group CJFh=U in the presence of a peroiryeen compouncl or other oxidizing agent as catalyst. Such polymerizabie monoolefimc compounds include the vinyl compounds, such as styrene and other vinylaryls. vinyl esters of carboxylic acids, vinyl eaters of inorganic acids including vinyl chloride anti other vinyl halides, vinylidene halides, acrylic acid and its derivatives, e. on, chloracrylic acid, methyl methacrylate, acrylonitrile (vinyl cy ankle) and the like.

accuse The preferred polymerization catalysts are organic peroxides, peracids and their-salts and inorganic peroxides including hydrogen peroxide. These may be activated by addition of various reducing agents, e. g. sulfoxy compounds such as soluble sulfltes, formaldehyde sulfoxylate, and the like. In such activated systems, the oxidationreduction potential can be regulated by relative rates of feed of catalyst and activator into the reaction mixture. While useful potential ranges have been indicated in the foregoing example and table. such values are relative to other operating conditions. For example, a change in pH will change the oxidation-reduction potentials. It is therefore necessary when applying these controls to the desired system that determination by trial he made sothat the" upper, lower and operating ranges are known. Thereafter, measurements will make it possible to operate in the desired range and with the requisite catalyst present.

The calomel half cell is primarily a reference electrode only, and the changes in potential largely involve the platinum electrode. Other electrodes such as silver-silver chloride for certain systems which could tolerate a fixed amount of chloride ion could replace the calomel half cell. Tungsten, carbon, antimony and other commonly employed electrodes may replace the platinum electrode. It will be understood that. as described above, the useful potential range must be located by trial.

in the presence of water, related solvents such as alcohols, or mixtures of these may also be employed whenever the electrode system responds sumclently to the oxidation-reduction character of the mixture.

The method is a valuable one for controlling the viscosity. molecular weight, solubility and other polymer characteristics whichvary with the conditions under which it is prepared and especially those which vary with catalyst concentration.

Iclalm:

l. A process for polymerizing vinyl acetate in aqueous emulsion in the presence of hydrogen peroxide as catalyst and formaldehyde sulfoxylate' as activator therefore characterized in that the relative concentrations of said peroxide and sulfoxyiaie are controlled in response to measurements of the oxidation-reduction potential of-the reaction mixture within a range not exceeding 200 millivolts.

2. A-process for polymerizing a vinyl compound in aqueous emulsion in the presence of a peroxygen compound as catalyst and a sulfoxy reducing compound as activator therefor, characterized ethal. the relative concentration of said perox'ygen compound and reducing compound are controlled in response to measurements of the oxidation-reduction potential of the reaction mixture within a range not exceeding 200 mild volts.

3. A process for polymerizing a vinyl ester in aqueous emulsion in the presence of a peroxide as catalyst and a sulfoxylate as activator therefor, characterized in that the relative concentrations of said peroxide and sulfoxylate are-controlled in response to measurements of the oxidation-reduction potential of the reaction mixture within a range not exceeding 200 millivolts.

. JAMES H. YOUNG.

REFERENCES CITED The following references are of record in the file of this patent:

um s'rs'rns Psm'rs Stewart July 31, 1945 

1. A PROCESS FOR POLYMERIZING VINYL ACETATE IN AQUEOUS EMULSION IN THE PRESENCE OF HYDROGEN PERIOXIDE AS CATALYST AND FORMALDEHYDE SULFOXYLATE AS ACTIVATOR THEREFORE CHARACTERIZED IN THAT THE RELATIVE CONCENTRATIONS OF SAID PEROXIDE AND SULFOXYLATE ARE CONTROLLED IN RESPONSE TO MEASUREMENTS OF THE OXIDATION-REDUCTION POTENTIAL OF THE REACTION MIXTURE WITHIN A RANGE NOT EXCEEDING 200 MILLIVOLTS. 